We have developed a line of mice bearing a targeted mutation in the TATA-binding protein (TBP) that replaces the endogenous gene with a version that is identical except it produces a protein lacking 111 of the first 135 amino acids of the protein. Adult mice homozygous for this mutation (tbp ^N/^N are normal; however mutant fetuses suffer a very high rate of immune-mediated mid gestational miscarriages. We can rescue the mutants past this crisis in various ways, including: 1) providing them with wildtype extra embryonic tissues; 2) rearing them in severely immune compromised dams; or 3) disrupting fetal (2m expression in their placentas. Thus, these mice provide an important model system for studying both the fetal and the maternal side of the maternal/fetal immune interaction. We hypothesize that the maternal/fetal immune interaction involves the interplay between maternal immune cells and fetal genes expressed at the maternal/fetal interface in the placenta; alteration of either maternal or fetal players in this interaction can affect the outcome of pregnancy. In this study, we propose three Specific Aims: Aim 1, identify the cellular components of the maternal immune system that participate in rejection of tbp^N/^N fetuses; Aim 2, characterize expression of MHC-I family genes at the implantation sites of tbp+/+, tbp^N/+, and tbp^N/^N fetuses; and Aim 3, identify proteins that interact with the TBP N-terminus in placenta. Results obtained under Specific Aim 1 should reveal maternal factors that can compromise pregnancy. Results obtained under Specific Aim 2 are expected to reveal fetal gene expression defects that might compromise pregnancy. Discoveries made under Aims 1 and 2 could lead to novel therapeutic strategies for combating chronic miscarriages. Finally, results obtained under Specific Aim 3 are expected to reveal gene regulatory mechanisms that underlie expression defects which can compromise pregnancy. These results could lead to novel prognostic tools for predicting susceptibility to spontaneous miscarriages.